'It's the gift that keeps on taking'

When he first noticed his little finger shaking, Michael J Fox put it down to a hangover. A year later - at just 30 years of age - he was diagnosed with Parkinson's disease. He tells Emma Brockes why, despite it all, he's still smiling

After he was diagnosed with Parkinson's disease, but before he started writing books about optimism, Michael J Fox went through a period of seeing himself as he thought others saw him. "Peculiar," he says, was the overall impression. "Funny looking. [Parkinson's] makes me squirm and it makes my pants ride up so my socks are showing and my shoes fall off and I can't get the food up to my mouth when I want to." Fox had been a movie star for five years when he was diagnosed, and was used to being stared at. But of course this was different. "I hate the way it makes me look," he thought. "That means that I hate me."

Seventeen years after diagnosis, and it's still hard for him to predict exactly when his daily meds will kick in. Visitors prepare for a range of possibilities: if the drugs haven't taken effect, he becomes "akinetic", seized by tremors and stiffness. If the medication is working but coincides with a natural surge of the neurotransmitter dopamine, he goes the other way and becomes "dyskinesic", sending him "rocking, dipping, diving". Fox once appeared unmedicated before Congress, to illustrate the terrible effects of the disease, and describes how he looked "as if an invisible bully were harassing me as I read my statement". Today, he is on target and walks into his Manhattan office buff, trim and wearing a blue cashmere sweater, like a well-preserved French exchange student. It's tough to look louche with advanced-stage Parkinson's, but somehow Fox manages it.

If you were adolescent or thereabouts when Back To The Future came out in 1985, nothing that has happened to Fox in the years since will have unseated the image of him in that red body warmer, standing in a car park at midnight as the souped-up DeLorean hit 88mph and disappeared back to 1955. The cute little face, the Calvin Klein underpants, the soft sable hair (I was the target audience. Does it show?) - we were so short ourselves, we didn't even notice he was 5ft 4in, or, more incredibly, a 24-year-old playing a 17-year-old. He's 47 now and retains the heightened physical awareness of a tiny male movie star. Doctors told him it might even help with the Parkinson's. Where possible, Fox converts his tics into stock mannerisms: an arm will dock in his hair and smooth it back; a leg will end up balanced on one knee like someone casually repositioning. The effect is of someone with a boyish energy who has had too many Cokes, but even on bad days, says Fox, "I don't care. If I don't get food in my mouth, I'm still happy. If my pants are round my ankles, as long as I don't get arrested for indecent exposure, I'm happy. I'm worried about keeping my hair, not how it's combed."

Since he came out as a sufferer of the disease in 1998, and launched an impressive campaign to normalise its symptoms, Fox has become a pin-up for a certain kind of relentless brightness in the face of adversity. As he well knows, his first memoir, Lucky Man, could quite easily have been called Poor Bastard - there is certainly a market for that kind of book. Instead, Fox wrote of how, after seven years of denial and depression, he gradually came to terms with his diagnosis, set up the Michael J Fox Foundation, gave up drinking and started advocating on behalf of what he calls "Parkies". He is at such an advanced stage of acceptance that it can sound like evangelism, another form of denial - he calls the disease a "gift". But then, with the charm that made Lucky Man a bestseller, he adds sardonically, "the gift that keeps on taking".

Always Looking Up: The Adventures Of An Incurable Optimist is a follow-up volume, a loose account of his last 10 years. Fox planned it originally as a book-length study of optimism, before deciding he didn't have the necessary journalism skills and returning to memoir. It was written via dictation, as he paced up and down his office and his writing assistant took down his thoughts. He could control a pen sufficiently to correct the manuscript.

Much of the book is given over to how he got into campaigning for stem cell research, the hope of many Parkinson's sufferers and bugbear of the Christian right, which sees it as a moral equivalent to abortion. Stem cells are extracted from embryos a few days old that are produced through IVF, and which would in any case be destroyed. "There are 30,000 conditions and diseases that they think they might be able to address through stem cell research," Fox says, "but the thing is, the opportunity." On 9 March, when President Obama overturned Bush's freeze on research funding, Fox was filming a documentary in Bhutan. After years of campaigning, his satisfaction was tempered by the knowledge that eight precious years of potential advances had been lost. Now that the president is in favour, Fox observes wryly, "there is no money" for Congress to pay for it.

In the book, Fox strains so hard for a measured tone when writing about the former president that you can almost see the vein standing out on his forehead. "There's no sense in beating up George Bush," he says. "George Bush is gone."

Just for your own satisfaction, then. "I got that on 9 March."

He isn't so dainty about Rush Limbaugh, the far-right radio host who accused Fox of "exaggerating" his symptoms and "acting" in an election broadcast in 2006. Appearing on behalf of a pro-research Democrat in Missouri, Fox shocked audiences who hadn't seen him in public by swaying in his chair and speaking through the Parkinson's mask, a facial rigidity caused by the disease, all of which Limbaugh impersonated the next day on TV. Fox says that of course he was appalled by the man's crassness, and his mother, still living in Canada, had to be talked down from going to war, but "that's what Rush Limbaugh does. He has a very devoted following. The popular name for them is 'ditto-heads', because whatever he says, they say ditto. That's not a club I want to belong to, for anybody." Ultimately it worked in his favour, Fox says, because "we were able to harness that attention and there was a shift in public opinion about stem cells. We made some real headway.

"I personally like the way people - an athlete or an entertainer or a broadcaster or someone - can say something unbelievably politically incorrect, harmful, hurtful, nasty." He adds, pausing, "I really like it. Because it's, like, OK, now I know who you are."

It has been so long since Michael J Fox was a movie star that he's not sure his youngest children even know that's what he was, nor what he does for a living now. His eldest son, Sam, 19, is studying biology at college in California; his twin girls, Aquinnah and Schuyler, 14, go to high school in New York, and his baby, Esme, is eight. "I don't know that they've ever seen Back To The Future all the way through. Just as Parkinson's isn't a big topic of conversation in my house, neither is my career. I go down to my office every day and they say, 'Dad's going to work.'"

His office is opposite Central Park, in the same building as the family home. Fox met his wife, Tracy, on the set of Family Ties, the 80s sitcom that launched his career and in which she played his on-screen girlfriend. These were the early days of his fame, when he was out partying all the time. When Fox woke up one morning in 1990 and noticed his little finger shaking, he thought it was a side effect of a hangover. He was in a hotel room in Florida, where he was filming Doc Hollywood, and his life within the Hollywood bubble was supposed to be perfect. Instead, he felt miserable. "Space within the bubble would increase with every success and contract with every failure," he writes in Always Looking Up. He was drinking too much, was always away from home and, whenever he had a new film out, turned into a nervous wreck.

He didn't realise it at the time, Fox says, but he was living "in fear". In 1990, the Back To The Future franchise had finished, Family Ties had ended and he was at that difficult transitional stage between teen and adult movie star. He went to a doctor, who told him the finger was nothing to worry about and indulged Fox's theory that it had to do with an accident on the set of Back To the Future III, when he'd caught his neck in a rope. It was almost a year later, after every test had been exhausted, that he was told in a Manhattan doctor's office that he had early-onset Parkinson's disease, a degenerative illness with no cure. "Hide", Fox says, was his first reaction, and he stuck to it for as long as he could. The doctor said if he was lucky he could keep acting for another decade. Fox was 30 years old - 70% of Parkinson's sufferers are over 50.

The weird thing is, he says, that until that moment he had always felt lucky. Growing up an "army brat" in Canada, the fourth of five children, he was expected to go into low-paid manual work or at best something clerical. His father was a rigid figure whom the young Fox judged harshly for never taking any risks; after he left the army, he found work as a police dispatcher. His mother was a clerk in a storage plant. His role model was his grandmother, whom the family believed to be psychic. She told them her grandson was going to be famous and at 16, true to her words, he won a part playing a 12-year-old in a Canadian TV show. He was paid $6,000, "a shitload" of money to a family such as his, and it gave him the confidence to quit school without graduating and drive to LA. When he got there, he discovered the Screen Actors Guild already had a Michael Fox listed. Fox's middle name is Andrew, but Michael A Fox sounded ridiculous, he thought, so he went with a J. There were a few threadbare years as he scrounged for work, but not enough to shake his conviction in his own lucky genes. Then he won the part in Family Ties and off he went.

Fox's dismissal of his 20s as lost years is either a brave admission or the revision that validates the way he lives now. Surely he's too hard on his young self - regarding every morning he lay in bed with a hangover as a waste of a day? "I have a lot of compassion for my younger self. It's funny. I wouldn't have an appreciation for the things I do now if I didn't have those experiences. I was so... it really is a course correction - at that point in my life, when I got Parkinson's, I had to look at the way I was living: the drinking. It wasn't like a little warning sign at the side of the road. It was a big caution in flashing lights. I don't know that I would have the family that I have now, the life I have, the sense of purpose, if none of this had happened."

After he was diagnosed in 1991, Fox's drinking got much worse. The alarm call came a year later, when he woke up on the sofa one morning, stinking of booze, with his baby son crawling on him and half a can of beer on the floor next to him. When he opened one eye to see his wife looking down at him, she didn't seem angry or disgusted, but, worse, indifferent. Fox made arrangements that day to get help with his drinking and hasn't touched alcohol since. "No, I don't look back with wistfulness; I don't romanticise it." There is a poignant moment in the book, however, when, flicking through channels on late-night TV, he is "ambushed by the image of a younger, healthier me", and lingers too long before switching it off. Muhammad Ali, a fellow Parkinson's sufferer, is one of Fox's role models, along with Lance Armstrong and the late Christopher Reeve, and Fox rang Ali's wife, Lonnie, to ask about this particular thing, the horror of being confronted with the way you once were. "I was thinking, 'What does he think when he sees himself on television as he was as Cassius Clay? Ducking and weaving and joking and spouting poetry. Does he feel sadness? A sense of loss?'" Lonnie said, "He loves it. He loves to see himself. He can't get enough of it."

This is how Fox feels about himself. He can joke about being approached by drug dealers in the street who mistake his quivering for a junkie's comedown. On the other hand, he says, Parkinson's has made him a better poker player - no one can tell when he's bluffing. Does he have Parkinson's in his dreams? "I don't think I shake in my dreams. It's not... it's not connected to my ego."

The effect of those first seven years, when Fox was in deep denial and would, incredibly, film in front of a live studio audience every week on the sitcom Spin City, have been thoroughly expunged. He developed tricks to disguise his condition, anchoring himself to furniture, sitting on his hands and hiding behind props, and got so frustrated he punched holes in his dressing room wall. Finally, when the prospect of brain surgery loomed, he "came out" and, after a huge public response, tentatively began his second career as an advocate. When he filmed his final episode of Spin City in 2000, he knew it was probably the last regular acting job he would have. "I had been Mike the actor," he writes, "then Mike the actor with PD. Now was I just Mike with PD."

The work of the foundation and the success of his memoir have refreshed his fame since then. But in any case, after years of intense psychotherapy, he has changed his view of how the disease affects him. "The one choice I don't have is whether or not I have it. But beyond that my choices are infinite. How I approach it is up to me. It has a lot to do with - and this is hard for people to understand - accepting it. And that doesn't mean being resigned or not looking for a cure. But if you're trying to get away from it or change it, you're going to wear yourself out."

The Michael J Fox Foundation has become the leading Parkinson's fundraiser in the US, putting $140m into research over the last eight years. Would he run for office?

"Nah. I don't have the constitution for that. And I don't know that I want to be worrying about people's water supply and when the garbage trucks come."

To his surprise, he has had the chance to do some acting lately: a few episodes of Boston Legal and, at his friend Denis Leary's request, an appearance in Rescue Me, Leary's show about New York firefighters. "It felt good. I played a paraplegic, which is insane. It was nice to revisit [acting] again. But at the same time I didn't feel like, 'Aw, I'm home!' It was like visiting a place where you know the currency and the language, but you've moved on."

His children's attitudes seem to be as healthy as his. Fox's philosophy as a parent has always been "love 'em, feed 'em, keep 'em out of traffic". He thinks much of modern parenting is too fussy in that it tries to "protect them from everything... they're really sturdy little buggers. Emotionally, if you're honest with them, they can handle it." He has explained to each of his children that his brain works differently from theirs and they have accepted it and moved on. When he was writing his first book, his twins, then five, asked what it was about. "I guess it's about me," he said.

"About you being Shaky Dad?"

"Yeah."

"But Shaky Dad doing what? Riding a bicycle?"

He laughed and said, "Something like that."

I have one last question, although it's not really a question. That red body warmer in Back To The Future...

"The sea vest?"

Er, yes - everyone I know remembers it.

Fox always says he's flattered when people bring up his movie work, but he looks suddenly, infinitely weary. "The whole thing with Back To The Future was so strange. Eric Stoltz shot it for six weeks and then they hired me, wham bam, I was in the parking lot where they filmed the scene with the DeLorean and it was really last minute and it was cold and if it hadn't been I wouldn't have worn that vest. That whole look: those Guess jeans with the peg-legs and the high waist?" His self-scorn has found its appropriate level. "Ridiculous," he says.

• Always Looking Up: The Adventures Of An Incurable Optimist, by Michael J Fox, is published next week by Ebury Press. To order a copy for £17.99, including UK mainland p&p, call 0330 333 6846 or go to guardian.co.uk/bookshop